The use of "pulse 64 75" in the F100 program modulates the primary frequency with a 64hz wave at 75% duty cycle. This means that the square wave (which I always use and runs by default in the F100 series devices) is positive 75% of the time and 0 voltage 25% of the time when run in offset mode.

Turf, who runs the Yahoo group electroherbalism, first pointed out that this helps absorption of the frequency by the body or by pathogens in the body. Working with other clinicians, I have tested this out using the Aurameter on hundreds of people and found that for general purposes 64hz and 75% duty cycle work well.